Conventional staples are, typically, U-shaped and require a staple cartridge and anvil to fasten the staple onto a material. The U-shape of the staple can be considered relatively square-cornered because of the sharp angle at which the legs extend from the bridge. On activation of a stapling device, the staple legs are advanced forward so that they penetrate a material on both sides of a slit or opening. As a staple former is advanced further, the legs of the staple bend around the anvil causing the tips of the legs to advance along an arcuate path toward each other so that the staple ultimately assumes a generally rectangular shape, thereby compressing the material that has been trapped between the staple legs, which is tissue in surgical applications. This compression of the material is the mechanism by which a closure is effected. Depending on the length of the incision or opening, a series of staples will be delivered along its length, which can ensure a blood tight closure in surgical procedures.
Because the staple has two legs that pierce the material, they are well suited for fastening two or more layers of material together when used with the opposing anvil. Whether used in an office or during a surgical procedure, most staples 1 have similar shapes—a bridge 2 connecting two relatively parallel legs 4, which legs are disposed approximately orthogonal to the bridge 2, which, depending on the material of the staple, results in a square-cornered U-shape. In surgical stapling devices, it is beneficial to start the legs 4 in a slight outward orientation to assist retention of the staples within the cartridge. The staple illustrated in FIG. 1 is representative of conventional surgical staples. Such staples are compressed against an anvil to bend the tips of the legs 4 inward. For purposes sufficient in surgery, the final stapled configuration has a stapling range from a “least” acceptable orientation to a “greatest” acceptable orientation. The “least” acceptable staple range is a position where the tangent defined by the tip of each leg 4 is at a negative angle to a line parallel to the bridge 2 and touching the lower portions of both legs 4. The “greatest” acceptable staple range is a position where the legs 4 are bent into a shape similar to the letter “B.”
The staple 1 of FIG. 1 is shown in an orientation where the tips of the legs 4 are bent slightly by an anvil on the way towards a final stapled form. (This slightly bent orientation is also present with respect to the staples illustrated hereafter.) The legs 4 of such slightly bent staples have three different portions:                a connecting portion 6 (at which the legs 4 are connected to the bridge 2);        an intermediate portion 8 (at which the staple is bent; of course it is also possible for the connection portion 6 to be bent for various fastening purposes); and        a piercing portion 10 (for projecting through the material to be fastened; this portion, too, is bent when fastening).Many stapling devices exist to deploy such staples. Some surgical stapling instruments are described in U.S. Pat. No. 5,465,895 to Knodel et al., and U.S. Pat. Nos. 6,644,532 and 6,250,532 to Green et al. When the staple 1 is bent for fastening, the polygon formed by the interior sides of the bent staple 1 defines an envelope or a central region 14. The material to be fastened by the staple 1 resides in and is compressed within the central region 14 when stapling occurs. When the final staple orientation is B-shaped, there can be two regions in which the tissue is held and compressed.        
One common feature associated with conventional staples is that there is no controllable way of adjusting the compressive force that is applied by the staple to the material being stapled. While items such as paper and cardboard can withstand a wide range of stapler compressive force without breaking or puncturing, living tissue, such as the tissue to be fastened in a surgical procedure, has a limited range of compressive force and cannot withstand force greater than a upper limit within that range without causing tissue damage. In fact, the range of optimal stapling force for a given surgical stapling procedure is relatively small and varies substantially with the type of tissue being stapled.
While it may be true that the distance between the bending point of the legs and the bridge (see, e.g., span 12 in FIG. 1) can be increased to impart less force on material within the staple, this characteristic does not apply when living tissue having varying degrees of hardness, composition, and flexibility is the material being stapled. Even if the staple leg bending distance 12 is increased, if more or less or harder or softer tissue than expected is actually captured within the staple, the force applied to the captured tissue will not be controlled and will not be optimal for that tissue.
When one, two, or more layers of tissue are being stapled, it is desirable for the tissue to be at a desired compressive state so that a desirous medical change can occur, but not to be at an undesired compressive state sufficient to cause tissue necrosis. Because there is no way to precisely control the tissue that is being placed within the staple, it is not possible to ensure that the tissue is stapled within an optimal tissue compression range, referred to as an OTC range. Therefore, ruling out of tissue necrosis is difficult or not possible. Further, tissue presented within one staple may not be the same tissue that is presented within an adjacent staple or is within another staple that is fired during the same stapling procedure. Thus, while one or a few of a set of staples could actually fasten within the OTC range, it is quite possible for many other staples in the same stapling procedure to fasten outside the OTC range.
What is needed, therefore, is an improved staple and improved methods of stapling that allow automatic control of the staple compression force imparted upon the material being stapled so that compression of the material remains within a desired OTC range. While prior art surgical stapling instruments have utility, and may be successfully employed in many medical procedures, it is desirable to enhance their operation with the ability to deliver a staple that can automatically tailor the compression force delivered to the tissue without external mechanics or operations.